Sequence boost circuit for discharge lamps



Sept. 23, 1958 C. E. WILLIAMS SEQUENCE BOOST CIRCUIT- FOR' DISCHARGELAMPS Filed Feb. 2, 1954 '2 Sheets-Sheet 1 Sept. 23, 1958 c. E. WILLIAMSSEQUENCE BOOST CIRCUIT FOR DISCHARGE LAMPS 2 Shets-Shet 2 Filed Feb. 2,1954 m .Im Y PM e 0W m t o m v s .f u n nk n s K l r s M U E M n e c 0 AM a L L A a m M u O T U C U V w D L WTV W 1 v m Y m n a m .nu N u" T EHM- E ma A 5 U n v mwfiig ww MGEi H6 o 2 4 v 5 A a k Charles E. Williams,Stanmore, England, assignor to General Electric Company, a corporationof New York Application February 2, 1954, Serial No. 407,637

Claims priority, application Great Britain April 16, 1953 3 Claims. (Cl.315-97) This invention relates to circuit arrangements for starting andoperating from an alternating supply electric discharge devices having agas or vapour filling. It relates more particularly, though notexclusively, to arrange ments for starting and operating low pressureelectric discharge lamps, such as the well known fluorescent lamps.

In electric discharge devices of the instant kind, the voltage requiredto be applied between the electrodes of the device for starting thedischarge (hereinafter referred to as the starting voltage) isconsiderably greater than the voltage required between the electrodesfor maintaining the discharge when started (hereinafter referred to asthe running voltage). In addition, such devices have inherently anegative characteristic in operation and require to be operated inseries with a ballast impedance which will give the arrangement anover-all positive characteristic. 7

In cases where the steady operating voltage normally applied between theelectrodes prior to starting is less than the starting voltage of thedevice, some form of starting means is required. A form of such meanswidely used at present is a starting switch connected between theelectrodes of the device. This switch is initially closed to produce aflow of current through a choke providing part or the whole of theballast impedance. It is thereafter opened to produce an inductive kickacross the choke which provides a voltage pulse between the electrodesof the device which exceeds the starting voltage and causes thedischarge to start.

In the .case of two devices operated in'series, similar considerationsapply, regarding the two devices as equiva lent to a single device whosestarting and running voltages are the sum of the starting and runningvoltages, respectively, of the two devices. However, when the steadyoperating voltage available is less than the sum of the startingvoltages but greater than the individual starting voltages, analternative method of starting, usually referred to as sequencestarting, is sometimes used. In sequence start arrangements the twodevices are connected to the source of operating voltage in series witheach other and with a suitable ballast impedance, and the junctionbetween the devices is also connected to the source of operating voltagethrough a starting impedance, usually a capacitor. At starting the wholeof the operating voltage is first applied across only onedevice and.causes that device to start, whereupon the residual operating voltage,other than that dropped across the started lamp, is automaticallyapplied between the terminals of the second device and causes thatdevice to start. The starting impedance is arranged to be of relativelyhigh value so as to draw a negligibly small current in normal operationof the two devices.

The object of this invention is to provide a circuit arrangement forstarting and operating two devices in series which incorporates animproved form of starting means. It will be seen that the arrangement inaccordance with the invention effects a sequence starting of the UnitedStates Patent" devices but operates in a different manner from the knownsequence start arrangements.

According to the invention in a circuit arrangement designed forstarting and operating two electric discharge devices from analternating supply of a given frequency, the said devices are connectedin series with each other and with a ballast choke forming part or thewhole of the ballast impedance for the two devices. A by-pass capacitoris shunted across one of the devices, said capacitor being connected onone side to a tapping or tap point on said choke and being of suchcapacity that the capacitor and the tapped-off part of the choke whichlies in seriestherewith with respect to the supply form a seriesresonantcircuit whose resonant frequency is higher than the supply frequency.The arrangement is such that in use and at starting substantially thewhole of the operating voltage is first applied through the by-passcapacitor to one device to effect starting thereof. Thereafter saidseries-resonant circuit is excited by virtue of the nonsinusoidal natureof the waveform of the voltage appearing across the started device so asto produce by step-up autotransformer action of the tapped choke aresultant alternating voltage across the second device whose peak valueis greater than it would be if the tapped-off part of the choke werereduced to zero and is such as to effect starting of the'second device.

The choke may in some cases provide the whole of the ballast impedancefor the two devices, but in other cases the choke may be included inseries with a ballast capactitor and form part of an over-allcapacitative ballast impedance. The latter form is in fact especiallyadvantageous when the operating voltage is not much greater.

than the combined running voltages of the two devices since more stableoperation,- relative to fluctuations in the supply voltage, is thenobtained than would be the case with an equivalent purely inductiveballast impedance.

The ohmic value of the by-pass capacitor at the supply frequency should,of course, be sufficiently large to ensure that a tolerably smallcurrent is drawn by it in steady operation of the devices. The positionof the tapping on the choke, that is to say the inductance of thetapped-0E portion and step-up ratio of the autotransformer formed 1thereby, and the capacity of the by-pass capacitor are preferably chosento obtain the maximum value of the peak voltage applied to the seconddevice. In view of the efiect on voltage waveform of the various circuitcomponents, the optimum values of the capacitor and tapping are bestdetermined by trial for each design of circuit. We have found that thebest results are usually obtained when the resonant frequency of theseries-resonant bypass circuit is about ten times the supply frequencyand the tapped-oh? part of the choke included in it is about V of thetotal inductance of the choke.

It will be appreciated that the tapping on the choke need not be aconnection to a point on a single winding; the, choke may in some casesbe formed with two series-connected windings with the tapping point towhich the bypass capacitor is connected located between these windings.The expression tapped-01f part of the chokereduced to zero in theforegoing statement of the invention is intended to mean that thetapping point is to be regarded as moved to the corresponding end of thechoke and not that the tapped-01f part of the choke is to be regarded asremoved.

The invention will be further explained with reference to theaccompanying drawings, in which:

Fig. 1 shows schematically one circuit arrangement in accordance withthe invention;

Figs. 2, 3, 4 and 5 are diagrams explanatory of the operation of-thearrangement; and

Fig. 6 shows another circuit arrangement in accordance with theinvention.

Referring now to Fig. 1, the arrangement shown comprises two'tubularelectric discharge lamps L and L of the positive column type having afilling of inert gas at a few millimeters pressure, The filling mayinclude mercury for'providing a mercury vapor discharge in operation,and the lamp envelopes in-such case are coated and are connected to themain secondary winding of a step-up autotransformer W (which serves alsoas a filament'heatingtransformer), in series with an iron-cored ballastchoke B and a ballast capacitor C which are a such that the over-allballast impedance is capacitive.

' The primary winding of the transformer W. is connected to the circuitinput'terminals P and N, represent- -ing the phase and neutralterminals, respectively, or, in 1 other words, the high and low sides,respectively, of the windings S and S and the adjacent cathodes of thelamps are connected to a-common electrode heating secondary winding S ofthe transformer W. The lamps L and L may-be providedwith'earthedstarting strips (not shown) for facilitating-starting andare shunted by :radio interference suppression capacitors C and C of lowcapacitance.

In accordance withthe invention, a tapping T on the choke B is connectedthrough a by-pass capacitor C to the junction of thelamps L and L sothat the arrangement operates substantially in the following manner. At

tially the whole of the operating voltage, which in this case is thestepped-up supply voltage, is first applied to the lamp L throughthe'by-pass capacitor C and this causes the lamp to start.

Lamp L alone being started, the voltage which then two 5-foot, 80-wattlow pressure mercury vapor fluorescent lamps of 1 /2 inche's' diameterfrom a'250-voltf50- cycle mains supply using" a choke B of totalinductance 0.795 henry and a ballast capacitor C of capacity 6microfarads. The capacity of the by-pass capacitor C was 1 microfaradand.;the. value of the tapped-off part I of the choke was 0.0318 henry.The filament heating transformer-secondary windings S S2 and 8;, werearranged to give a total step-up of 32 volts in the voltage nppliedacross the... two lamps. .a'nduthe :autotransforrner W wasarrangedutostep-up the supply'voltage by volts.

In a modification of the circuit arrangementof-Fig. 1, for operation onthe same supply, the capacitor C was omitted to: provide an.inductiveaballast for thelamps and the following alternativevalues forthe circuit compoucnts in question'were used:

Total inductance of choke B henr 0.71 V supply. Thenonad acent cathodesof the lamps L and inductanceu of: tappedqofil part t i 0,0284 L- areconnected to separate electrode heating secondary capacity.ofbyqpassapacitorC4 ;micmfaradn 1 :Step-up of:supply voltage provided-by' the autotransformer W a volts capacitor C acts also to some extentto correct the power factor and reduces the valueof the powerfactor:.correction capacitor required. v

Referring now to Fig. 6, this shows another modification of thearrangement of Fig. l in which the, ballast choke B and ballastcapacitor C .are..includedbetween "the lamps. The mode of operation ofthis further modification is similar to that oflFig. 1 and correspondingreference numerals in the two figures represent-correspending parts. Thecommon electrode heatingwinding S for the adjacent electrodes of thelamps is'now replaced by the separate heating windings S and 8 appearsacross it is nonsinusoidal and has approximately It will be appreciatedthat the invention isnot limited the waveform shown in Fig. 2. In thisfigure, and also in 40 to use with devices having heatable electrodes.and can Figs. 3; 4 and S,--the ordinates represent voltage and the beapplied with lamps, or other devices, of. the .coldabscissae time. Thewavefront at a-isof the steeply cathode or nonheated thermionic cathodetype. .Also falling kind suitableforexcitingoscillationof'the serieseach of the two devices in a circuit arrangement in acresonant circuitconstituted by the capacitor C and'the cordance with the invention ashereinbefore described tapped-off part t-ofthe choke B. Theoscillations'are may be replaced by two or more lamps in series. It is---excited across the part fot the choke andare ofthe'nature intendedthat these and other. modifications of similar shown i'HFig Z; 'os illaflns-b ing damp d because of nature be included within the presentinvention whose energy y' fi p z y 105888 in scope is to be determinedby the appended claims. thechokc- What I claim as new and desire tosecure by'Letters 1 --'Ihe voltage" which would appear across, thesecond .5 patent f the U i d States i p at h i pp fp i Chokewerefedllced 1. In combination, an alternating current supply .of i "F FI h the resultant given frequency, a pair of gaseous electric dischargedet which ism f k pp p L1; being vices each having two-terminalpreheatable electrodes, a thecombinatiom o g m w 4 ballast inductance,said devices and said inductance being with awbltag fth 'f wn inFig. 3amplified by connected in series across said supply, means supplyingthe-autotransformeractioniofthe choke B. It willbe seen preheat t t idle t od 9, tap point in id that P valueof"thevoltage"available forstarting inductance between relatively close-coupled portions, a theamp. 1" -increased f mthe' lu r' g 4 t0 by-pass capacitor connected tosaid tap point and shunted the .valu'e'V in-Fig. 5. across one of saiddevices to apply initially a higher volto g flvailabla f' i the SECOildC9 age across the other device tostart it, said capacitor being pbiutililed fofrcndering the a i more proportioned relative to thetapped-off portion-of said iniailla'ndless dePendent, I P Pp y Voltageductance to'effect series resonance therewith at a frevariations-andonCXtCIIIEllCOIlditiOHSjSUCh ashurnidity. quency, hi h h th u lyfrequency, whereby the n' c h r hand it mayzbemtilizedm enable mp ofnonsinusoidal voltage developed across said other device -givenstartingvoltages to-be run-withloweroperating -voltages than-consideredpracticable hitherto. AlternatiVCIYy-With a-givenoperatingwoltage; it'may beutilized to enable lamps of higher starting voltagesthan hithertoconsidered practicable ,for thatoperating voltage, to be operatedsatisfactorily; -In-;either case the advantage is 'attained that theballast choke is required to dr0p a smaller voltage than inthe'comparable known arrangements and may be'constructed more cheaply.

By way of example, ina circuit. arrangementjof the kind shown in'Fig.1', it was found ,pos'sible:to..-,operate pair of gaseous electricdischarge :deviceseach having two-terminal preheata'ble electrodes, aballastinductance, saiddevices and said inductance being connectedtinseries across said output circuit; auxiliary windings. irrsaidtransforming-1 means connected. across saidelectrodes to providepreheating current thereto, a tap point in said inductance betweenrelatively close-coupled portions, a bypass capacitor connected to saidtap point and shunted across one of said devices to apply initially ahigher voltage across the other device to start it, said capacitor beingproportioned relative to the tapped-0E portion of said inductance toeffect series resonance therewith at a frequency higher than the supplyfrequency, whereby the nonsinusoidal voltage developed across said otherdevice after it has started produces damped oscillations in saidinductance which increase the starting voltage across said one device.

3. In combination, an alternating current supply of given frequency,transforming means having an input circuit connected to said supply andan output circuit, a pair of gaseous electric discharge devices eachhaving two-terminal preheatable electrodes, said devices and saidinductance being connected in series across said output circuit,preheating windings in said transforming means connected across saidelectrodes to provide preheating current thereto, a tap point in saidinductance between relatively close-coupled portions, a by-passcapacitor having one side connected to said tap point and shunted acrossone of said devices to apply initially a higher voltage across the otherdevice to start it, said capacitor being proportioned relative to thetapped-oil portion of said inductance to effect series resonancetherewith at a frequency about ten times higher than the supplyfrequency in order to increase the starting voltage across said onedevice after said other device has started.

References Cited in the file of this patent UNITED STATES PATENTS2,301,671 Abadie Nov. 10, 1942 2,436,399 Nathanson Feb. 24, 19482,496,981 Boucher Feb. 7, 1950 2,504,548 Lemmers a Apr. 18, 19502,611,885 Bridges Sept. 23, 1952

